Determination of the feeding route of the hottest

Determination of NC milling feed route

reasonable selection of feed route can not only improve the cutting efficiency, but also improve the surface accuracy of parts. When determining the feed route, we should first follow the principles required by the NC process. For CNC milling machine, we should also focus on several aspects: to ensure the machining accuracy and surface roughness of parts; Making the cutting route shortest can not only simplify the program segment, but also reduce the tool idle travel time and improve the processing efficiency; The numerical calculation should be simple and the number of program segments should be small, so as to reduce the programming workload

(1) feeding route of milling plane parts

when milling the outer contour of plane parts, the side edge of end mills is generally used for cutting. In order to reduce the trace of tool receiving and ensure the surface quality of parts, the cutting in and cutting out procedures of tools need to be carefully designed

when milling the contour of the outer surface, as shown in Figure 1, the cutting in and cutting out points of the milling cutter should cut in and cut out the surface of the part along the extension line of the contour curve of the part, rather than directly cutting into the part along the normal direction, so as to avoid scratches on the machined surface and ensure the smooth contour of the part

Figure 1 extension during cutting in and cutting out of the tool

when milling the inner contour surface of the closed attachment whose quality can be determined by the clamping degree of the sample, if the inner contour curve allows extension, it should be cut in and cut out along the tangent direction. If the inner contour curve does not allow extension (see Figure 2), the tool can only cut in and out along the normal direction of the inner contour curve, and its cutting in and cutting out points are selected at the intersection of the two geometric elements of the part contour. When the internal geometric elements are tangent without intersection (see Figure 3), in order to prevent the notch at the contour corner when the cutter compensation is cancelled (see Figure 3 (a)), the cutting point of the cutter should be far away from the corner (see Figure 3 (b))

Fig. 2 cutting in and cutting out of the inner contour machining tool

Fig. 3 cutting in and cutting out of the inner contour machining tool without intersection

Fig. 4 shows the tool path when milling the excircle by arc interpolation. When the round machining is completed, do not retreat the tool at the tangent point, but let the tool move a long distance along the tangent direction, so as to avoid the collision between the tool and the workpiece surface when canceling the tool compensation, resulting in the scrapping of the workpiece. The principle of cutting in from the tangential direction should also be followed when milling the inner arc. It is best to arrange the processing route from the arc to the arc (see Figure 5), which can improve the processing accuracy and quality of the inner hole surface

Figure 4 outer circle milling

Figure 5 inner circle milling

(2) machining route for milling curved surface parts

in machining, we often encounter various curved surface parts, such as molds, blades, propellers, etc. Because the surface of this kind of parts is complex and requires multi coordinate linkage processing, CNC milling machines and CNC machining centers are often used for processing

① ruled surface processing

for ruled surface with open boundary, ball head cutter is often used for "line cutting" processing, that is, the tangent path between the cutter and the part contour is line by line, and the line spacing is determined according to the part processing accuracy requirements. As shown in Figure 6, two processing routes can be used for engine large blades. When using the processing scheme in Figure 6 (a), each time machining along a straight line, the calculation of the tool location is simple, the program is few, and the processing process conforms to the formation of the ruled surface, which can accurately ensure the straightness of the bus. When the processing scheme shown in Fig. 6 (b) is adopted, it conforms to the data given by such parts, which is convenient for post processing inspection. The accuracy of leaf shape is high, but there are many procedures. Because the boundary of curved surface parts is open and there are no other surface restrictions, the curved surface boundary can be extended, and the ball head cutter should be machined outside the boundary

(a) feed along a straight line (b) feed along a curve

Figure 6 processing route of ruled surface

② surface contour processing

three dimensional surface processing should adopt different milling methods according to the surface shape, tool shape and accuracy requirements

the three coordinate line cutting method with two coordinate linkage processes any two axes of the X, y and Z axes for linkage interpolation, and the third axis for separate periodic feed, which is called two axis half coordinate linkage. As shown in Figure 7, the X direction is divided into several segments, and the round head milling cutter is milled along the curve cut by the YZ surface. Each segment is processed and fed Δ 10. Then machining another adjacent curve, so that the whole surface can be machined by cutting in turn. In the line cutting method, it should be selected according to the requirements of contour surface roughness and the principle that the cutter head does not interfere with adjacent surfaces Δ X。 Ball end milling cutter is usually used in line cutting. The cutter head radius of ball end milling cutter should be larger, which is conducive to heat dissipation, but the cutter head radius should not be greater than the minimum curvature radius of the surface

Figure 7 surface line cutting method

when machining a surface with a ball end milling cutter, it is always programmed with the data of the tool center path. Fig. 8 is the schematic diagram of tool center track and cutting point track of two axis half coordinate machining. ABCD is the surface to be machined, the pyz plane is a tangent plane parallel to the YZ coordinate plane, and its tool center trajectory O1O2 is the intersection of the equidistant surface IJKL of the surface ABCD and the plane pyz. Obviously, O1O2 is a plane curve. In this case, the curvature change of the surface will cause the position of the ball cutter and the cutting point of the surface to change, so the line ab of the cutting point is a spatial curve, thus forming twisted residual grooves on the surface

Fig. 8 two axis half coordinate machining Fig. 9 three axis machining

because the tool center path of two axis half coordinate machining is a plane curve, the programming calculation is relatively simple, and the NC logic device is not complex. It is often used in rough machining with little curvature change and low accuracy requirements

three axis linkage machining x, y and Z axes can be interpolated at the same time. When machining curved surfaces with three coordinate linkage, there is no possibility of large-scale resumption of production in domestic mines in a short time, and the line cutting method is usually also used. As shown in Figure 9, the pyz plane is a line tangent plane parallel to the YZ coordinate plane, and its intersection with the surface is ab. if AB is required to be a plane curve, the cutting point of the ball cutter and the surface should always be on the plane curve AB (i.e. cutting along AB) to obtain regular residual grooves. Obviously, the tool center trajectory O1O2 at this time is not on the pyz plane, but a spatial surface (actually a spatial polyline), so the X, y, Z axis linkage is required

three axis linkage machining is often used for the precise machining of complex spatial surfaces (such as precision forging dies), but the programming calculation is relatively complex, and the numerical control device of the machine tool used must also have the function of three axis linkage

the workpiece is processed in four coordinates as shown in Figure 10, and the side is a ruled twisted surface. If the round end milling cutter is used on the machine tool with three coordinate linkage to process according to the line cutting method, not only the production efficiency is low, but also the surface roughness is large. For this reason, the cylindrical milling cutter is used for peripheral cutting, and the four coordinate milling machine is used for processing. That is, in addition to the three rectangular coordinate movements, in order to ensure that the tool and the workpiece surface always fit together in the full length, the tool should also swing around O1 (or O2). China has been firmly in the forefront of the world. Because the swing angle movement causes the rectangular coordinates (y-axis in the figure) to need additional movement, its programming calculation is more complex

Figure 10 four axis half coordinate machining

five coordinate machining propeller is one of the typical parts of five coordinate machining, and its blade shape and machining principle are shown in Figure 11. On the cylindrical surface with radius R1, the intersection line AB with the blade surface is part of the helix, and the helix rise angle is Ψ i. Inclination of radial blade profile (axial secant) EF of blade α Is the caster angle. Helix AB is processed in polar coordinates and approximated by broken lines but cannot be copied. The approximation segment Mn is rotated by the C coordinate Δθ And Z coordinate displacement Δ Synthesis of Z. When AB machining is completed, the tool radial displacement Δ X (change R1), then process another adjacent leaf profile, and then process it in turn to form the whole leaf surface. Because the curvature radius of the blade surface is large, face milling cutter is often used to improve productivity and simplify the program. Therefore, in order to ensure that the end face of the milling cutter always fits the surface, the milling cutter should also be formed by coordinates a and B θ 1 and α 1. At the same time of swinging the angle, the additional movement of rectangular coordinates should be made to ensure that the end face of the milling cutter is always at the position specified by the programmed value, that is, at the cutting forming point, the plane of the milling cutter end is tangent to the surface to be cut, and the axis line of the milling cutter is consistent with the normal of the point of the surface, so five setting marks are required. The programming calculation of this kind of machining is quite complex, and automatic programming is generally used

Figure 11 propeller is processed in five coordinates

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